1. Field of the Invention
The present invention relates to electrical enclosures and frames, and in particular, to an electrical enclosure having a seismic subframe.
2. Prior Art
Electrical enclosure systems such as are used in connection with large or small electrical switchboard systems are commonly used to house a plurality of interior mounting boards for holding electrical components and other accessories for a wide variety of purposes. Manufacturing of such enclosures requires adaptability to various customer demands while providing an enclosure that is versatile, space efficient, and has an easily accessible interior. It is important that such enclosures have easily removable subpanel mounting boards that can be installed, removed or repositioned easily to minimize time and labor. Enclosures should be adaptable to multiple configurations and be inexpensive to manufacture. A sample of such an enclosure is shown in U.S. Pat. No. 5,292,189 to Lau et al. The base sections of the enclosure form a continuous rectangular guide channel around the inner periphery of the enclosure. In opposite parallel channel segments are received a pair of channel followers that are connected to opposite lower corners of the mounting board. The system provides a highly versatile and efficient enclosure and mounting system.
It can be appreciated however, that although such enclosures and systems perform very well in meeting normal design criteria, higher standards must be met in earthquake prone areas. Equipment used in earthquake zones must be able to meet the requirements for network building systems as outlined in Section 4.4 of the October, 1995 issue of Bellcore Standard GR-63-CORE. While prior enclosures and frames have been successful in providing flexible enclosures with easy accessibility, such systems may not meet the tougher earthquake requirements as outlined in the Bellcore Standard. The framework should be constructed to sustain earthquake equivalent forces without permanent structural or mechanical damage while also minimizing the deflection of the frame during such situations. In addition, it is advantageous for the framework to be a solid welded construction that mounts to an existing frame.
An example of a seismic frame is shown in German Patent DE19615759A1. The seismic frame includes various supports and braces which attach to the existing framework. However, the elements bolt onto the existing framework rather than weld on for added rigidity. Moreover, the various pieces extend between upright frame sections and block some of the opening at the front and rear of the framework, decreasing accessibility. In addition, the design may not meet all criteria for earthquake prone zones. The bolted on braces do not provide any bracing from the door or rear panel of the enclosure to the frame.
It can be seen that a new and improved cabinet and frame is needed that provides access and versatility as well as meeting the physical and functional performance requirements for use in earthquake environments. The present invention addresses these as well as other problems associated with electrical enclosures and frameworks.